1. Field of the Invention
The present invention relates to a long-life welding electrode and a fixing structure for the same, a welding head, and to a welding method.
2. Description of the Related Art
Conventional types of electrodes for welding are divided to those each having a sharp tip and those each having a flat tip. And in electrodes for welding having a sharp tip, the form remarkably changes during use and the durability is low, while, in those having a flat chip, the form little changes, but the arc discharge characteristic is remarkably degraded, and for the reasons as described above, in both types of electrode for welding, the frequency of exchange and replacement is high and the work efficiency is low.
In a conventional type of electrode 901 having a flat tip at shown in FIG. 9(b), there are a number of points at which a distance between the welding electrode 901 and a welded object 910 becomes shortest (arc grounding point:), and a point, from which an arc discharge is generated (arc discharge point:), at various points, so that an arc used for welding can not be kept stable.
Also, a welding electrode is worn out along a form of an equipotential surface, and it has been found out that a welding electrode having a sharp tip (with an angle from 30 to 60 degrees), is easily worn out and it is impossible to execute welding for a long time under stable conditions.
On the other hand, it has been tried to develop a technology of adding around 2 weight % of ThO2 (thoria) in a base material for a welding electrode (W) for the purpose to improve durability of the electrode.
When thoria is added, sometimes the durability may be improved, but the durability is not always improved. That is to say, the effect provided by adding thoria is not constant.
Conventionally, a welding electrode is fixed with a screw. That is to say, as shown in FIG. 2, a welding electrode 201 is fixed to a fixing base 202 by inserting the welding electrode 201 into an inserting section 204 of a fixing base 202 having the inserting section 204 and also passing a set screw 203 through a screw hole provided in a side of the fixing base 202.
With the conventional type of fixing structure as described above, however, the welding electrode is degraded.
Generally argon in used as a welding gas, but argon is poor in its thermal conductivity, and high a current value is required for welding, so that a temperature of the welding electrode increases and durability of the electrode is worsened.
Further, a welding gas is supplied via a welding power supply unit with a resin-based material emitting a large quantity of gas used in piping in the power supply unit. Also a resin-based material is used for a tube for connection among a gas supply system, a welding power supply unit, and a welding head, so that local atmosphere is worsened by the resin material during welding and the welding electrode may be oxidized and degraded (Refer to FIG. 6).
Engineers are required for replacement of a degraded electrode, and many engineers are required for the conventional type of electrodes each frequently requiring replacement, further, a long time is required for this work for replacement, so that the work efficiency is low, which does now allow welding with high reliability.